Study on the influence of vertical stress difference coefficient on fracture characteristics of shale under high stress

IF 3.5 3区 工程技术 Q3 ENERGY & FUELS Energy Science & Engineering Pub Date : 2024-07-31 DOI:10.1002/ese3.1819
Xin Chang, Guozhou Qiu, Jing Li, Yintong Guo, Zhiwen Hu, Hanzhi Yang, Xinao Zhang, Yongjiang Liu
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Abstract

To study the effect of vertical stress difference coefficient on fracture characteristics of shale fracturing, high stress true triaxial hydraulic fracturing test was carried out. By analyzing the profile after fracturing, it was found that the area of hydraulic fracture increased with the increase of vertical stress difference coefficient, and the probability of shear fracture will increase when the stress difference coefficient was high. A high vertical stress differential coefficient exerts a strong control over the direction of crack propagation, while a low vertical stress difference coefficient is beneficial to improve the roughness of hydraulic fracture surface and promote the formation of complex fracture network. By analyzing the pump pressure curves of different tests, it was found that with the increase of vertical stress difference coefficient, the formation and expansion of hydraulic fractures were more difficult. The surface characteristics of hydraulic fractures were quantified based on three-dimensional topography scanning technology, combined with fractal dimension and fracture area calculation method, the results showed that with the increase of vertical stress difference coefficient, the fractal dimension and fracture area decreased. Since shale is stratified, and the transformation of reservoir is mainly reflected in the enhancement of fracture complexity through tensile failure, Xsite discrete grid method was used to study the influence of fracture propagation behavior with different bedding strengths. The results showed that when the bedding tensile strength was high, hydraulic fractures were easy to pass through the bedding, and when the bedding tensile strength was low, hydraulic fractures were easy to be captured by natural fractures. In addition, tensile cracks were easy to form when the tensile strength of bedding was low, shear cracks were easy to form when the strength of bedding was high, and the fracture volume was larger when the strength of bedding was low. This study provides a theoretical basis for hydraulic fracturing in engineering.

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研究垂直应力差系数对高应力下页岩断裂特征的影响
为研究垂直应力差系数对页岩压裂裂缝特征的影响,进行了高应力真三轴水力压裂试验。通过分析压裂后的剖面发现,水力压裂面积随垂直应力差系数的增大而增大,应力差系数高时,剪切压裂的概率增大。高垂直应力差系数对裂缝扩展方向有较强的控制作用,而低垂直应力差系数则有利于提高水力压裂面的粗糙度,促进复杂压裂网的形成。通过分析不同试验的泵压曲线发现,随着垂直应力差系数的增大,水力裂缝的形成和扩展更加困难。基于三维地形扫描技术,结合分形维数和裂缝面积计算方法,对水力裂缝的表面特征进行了量化,结果表明,随着垂直应力差系数的增大,分形维数和裂缝面积减小。由于页岩是层状的,储层的转化主要体现在拉伸破坏对裂缝复杂性的增强,因此采用 Xsite 离散网格法研究了不同垫层强度对裂缝扩展行为的影响。结果表明,当垫层抗拉强度较高时,水力裂缝容易穿过垫层;当垫层抗拉强度较低时,水力裂缝容易被天然裂缝捕获。此外,垫层抗拉强度低时易形成拉伸裂缝,垫层强度高时易形成剪切裂缝,垫层强度低时裂缝体积较大。这项研究为水力压裂工程提供了理论依据。
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来源期刊
Energy Science & Engineering
Energy Science & Engineering Engineering-Safety, Risk, Reliability and Quality
CiteScore
6.80
自引率
7.90%
发文量
298
审稿时长
11 weeks
期刊介绍: Energy Science & Engineering is a peer reviewed, open access journal dedicated to fundamental and applied research on energy and supply and use. Published as a co-operative venture of Wiley and SCI (Society of Chemical Industry), the journal offers authors a fast route to publication and the ability to share their research with the widest possible audience of scientists, professionals and other interested people across the globe. Securing an affordable and low carbon energy supply is a critical challenge of the 21st century and the solutions will require collaboration between scientists and engineers worldwide. This new journal aims to facilitate collaboration and spark innovation in energy research and development. Due to the importance of this topic to society and economic development the journal will give priority to quality research papers that are accessible to a broad readership and discuss sustainable, state-of-the art approaches to shaping the future of energy. This multidisciplinary journal will appeal to all researchers and professionals working in any area of energy in academia, industry or government, including scientists, engineers, consultants, policy-makers, government officials, economists and corporate organisations.
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